This invention relates to a hydraulic shaft sealing arrangement for high-temperature applications, more particularly for concentric shafts of a gas turbine engine, to seal the high-pressure shaft bearing chamber located in the low-pressure zone and the low-pressure shaft against the high-pressure zone.
Hydraulic sealing arrangements, as is generally known, are used for contact-free sealing between two concentric, co-rotating shafts. In principle, such sealing arrangements can also be used with only one rotating shaft. The sealing arrangement normally consists of an essentially U-shaped annulus arranged on the inner circumference of the outer shaft which is filled with a fluidic sealing medium, preferably oil, supplied from the lubricating circuit of the respective engine by the effect of centrifugal force. A circumferential sealing fin arranged on the outer circumference of the inner shaft protrudes into the sealing medium in the annulus, thus providing a contact-free seal between the two shafts.
Such hydraulic sealing arrangements have proved good in many applications. In high-temperature applications, specifically the sealing of the bearing chamber for the high-pressure shaft and the low-pressure shaft of a gas turbine engine against the compressor air supplied at a temperature of 400° C., for example, these hydraulic sealing arrangements are problematic in that the oil, which is used as sealing medium and lubricant of the two shaft bearings, is liable to degradation and coking as a result of the high temperatures. In particular, on the side facing the high-temperature area, solid carbonization products will deposit on the inner surface of the annulus, which products may detach during operation and affect the continuous supply of fresh, cool oil into the annulus, the necessary dissipation of heat effected by the continuous oil exchange and, finally, sealing reliability.
Such a hydraulic sealing arrangement is described in Specification EP 1 045 178 A2, for example, in an application to the high-temperature area of a two-shaft gas turbine aircraft engine with concentric high-pressure and low-pressure shafts. The annulus containing the sealing medium into which the sealing fin of the low-pressure shaft protrudes is formed directly from the material of the high-pressure shaft. The considerable overall size and high weight of this design result in the known disadvantages for an aircraft engine. The annulus is continuously supplied with sealing medium, actually oil injected into the bearing chamber for lubrication of the rolling bearings of the high-pressure and the low-pressure shaft. A partial quantity of the sealing medium in the annulus is continuously drawn off either via an opening in the bottom or by means of a scooping plate from the bottom over the upper inner edge of the annulus. Continuous oil exchange prevents the sealing medium from being overheated, thus counteracting coking. Removal of the sealing medium from an annulus area formed into the bottom is, however, disadvantageous in that sealing against the hot high-pressure zone will be affected if the supply of oil and, thus, the amount of sealing medium in the annulus is inadequate. If the heated sealing medium is removed via the outermost edge of the annulus, the relatively hot sealing medium is passed over a considerable distance along the wall of an angular ring inserted into the annulus and the annulus inner wall, allowing oil carbon particles to deposit here as well. Even if the oil is continuously exchanged in the annulus, formation of a carbon layer on the hot inner wall of the annulus filled with sealing medium cannot be excluded.